114 OXY-HALOGEN ACIDS.
of the powder thus obtained with 75 g. of potassium dichromate
which has been dried by being melted. Heat the mixture in the
iron dish already used, whereupon the reaction will begin in spots
and spread with incandescence throughout the mass. Pulverize
the loose black product while still warm, cover it in a flask with a
warm mixture of 450 c.c. 80% ethyl alcohol and 50 c.c. of methyl
alcohol and boil it with a return condenser on the water bath for
two minutes. Decant the hot solution through a plaited filter into
a beaker, which is cooled with ice, and allow the salt to crystallize
while stirring. Using the mother-liquor from this crystallization
as a solvent, extract the black mass again in the same manner as
before; filter, and repeat the extraction three or four times.
Collect all of the cyanate crystals on the same suction filter, and
after washing with ether, dry them in a vacuum desiccator over
sulphuric acid. Yield, 30-40 grams. The product may be used
in the preparation of urea, or of semicarbazid, No. 123.
Urea from Ammonium Cyanate.
Ammonium cyanate when heated in aqueous solution undergoes a trans-
formation into urea (Wohler, 1828).
NH 4 CNO = CO(NH 2 ) 2.To carry out this classic reaction, evaporate a solution of 8.1 g.
potassium cyanate and 8.0 g. ammonium nitrate to dryness on the
water bath. Boil the powdered residue in a flask twice with alco-
hol, and concentrate the extract until a crystallization in fine, long
needles is obtained. Yield, about 5 g.
Heat a pinch of dry urea in a test-tube until it just melts, and
keep it at this temperature for about a minute; ammonia escapes.
Dissolve the residue in a little water and add a drop of copper sul-
phate solution and some sodium hydroxide, whereupon a rose-
violet coloration appears; this is the so-called biuret reaction.
(6) Oxy-halogen Acids.
- Electrolytic Production of Sodium Hypochlorite and Potassium
Chlorate.
Sodium hydroxide and chlorine react in cold, aqueous solution, forming
sodium hypochlorite, sodium chloride and water.
2 NaOH + Cl 2 = NaCl + NaCIO + H 2 O.
As soon as chlorine is present in excess, it reacts to produce free hypochlo-
rous acid,
HOH + Cls = HOC1 + HC1;